GMC 1996 Sierra Owner's Manual page 292

Fender Marker Lamps
(Dual Rear Wheel Pickup Models)
2. Turn the bulb socket
counterclockwise
and remove it from the
lens assembly.
3. Pull the bulb straight out of the socket.
4. Put
a new bulb into
the socket and push
it
in until
it is tight.
5.
Put
the socket back into the lens assembly and turn it
clockwise to tighten it.
6. Replace the lens and tighten the screws.
6-42